With the growth of wireless communication in recent times, frequency sharing and frequency reuse techniques are being encouraged worldwide by regulatory institutions, such as the Federal Communications Commission (FCC) in the United States of America. As an example, the FCC has mandated that in 2009 the broadcast of television (TV) signals shall change from analog to digital. When this occurs, the FCC has proposed that license-exempt devices can operate on unused portions of the newly unoccupied spectrum. A radio frequency management method known as opportunistic sharing is being considered for this spectrum. Specifically, the FCC has proposed to allow license-exempt communication devices to operate within portions of the television (TV) white space not used for broadcasts. Although this portion is not used for broadcasts, some low-power, licensed communication devices such as wireless microphones can also use this spectrum. Consequently, a license-exempt communication device that is unaware of the presence and proximity of the low-power licensed devices may cause interference. Thus, it is important that the licensed communication devices are protected from interference to avoid disruption in services.
One method of protection that can enable continued interference-free operation of the licensed, incumbent services and promote spectrum sharing with the license-exempt communication devices involves the use of beacon signals. Typically, a beaconing device in such a wireless communication network sends beacon signals on a beaconing channel or a beaconing sub-channel. A channel is defined to be a specific radio frequency band. Furthermore, a channel may be divided into sub-channels, where each sub-channel is radio frequency band within the band of the corresponding channel. One or more of these sub-channels may be used by a beaconing device for transmitting beacon signals. For sake of brevity, the term channel used herein may be used interchangeably with the term sub-channel unless explicitly noted otherwise. The beacon signal includes information about the beaconing device, such as the beaconing device's Media Access Control (MAC) address, the location of the beaconing device, the channels or sub-channels that are being used by the beaconing device or by the communication device associated with the beaconing device, the length of time that these channels will be used, the priority of the beaconing device, etc. This information can be used for various purposes such as synchronization, checking signal strength of the beaconing device and determining proximity to the licensed device. A communication device that wants to use a channel, such as a license-exempt communication device, may periodically monitor the RF spectrum to detect the presence or absence of beacon signals. If a beacon signal is heard on a beacon channel or a beacon sub-channel, then the communication device may not be able to use the corresponding channel indicated by the beacon signal for communication. Such a beacon signal is sometimes referred to as a “disabling” beacon signal.
Because a beacon signal serves as an authority to restrict access to a part of the RF spectrum, it is important that a communication device be able to determine the authenticity of a beacon signal. For instance, the beacon signal may be generated by a rogue, unlicensed beaconing device trying to cause a communication device to leave a channel. Motivations for a user operating such a rogue beaconing device may arise from a desire to clear the radio spectrum for use by a communication device, such as by indicating a falsely high priority level in the beacon signal, or a desire to simply cause other communication devices problems, such as by falsely indicating that a certain channel or set of channels is being used, for example, a denial-of-service attack.
To determine the authenticity of the beaconing device, the communication device listens to the entire beacon signal to acquire a signature of the beaconing device and a corresponding certificate granted to the beaconing device. In existing techniques, the communication device has to listen to the entire beacon signal to determine the authenticity of the beaconing device. However, any time spent listening to a beacon signal is wasteful, as communication devices sensing the beaconing channel or beacon sub-channels have to cease their normal operations to allow for a sensing module, which may reside in the communication device, to listen for a beacon signal. Such extended interruptions at the communication device may increase the latency in potentially time-sensitive applications and may also reduce the channel capacity.
Accordingly, it would be desirable to have a means of efficiently selecting a channel for communication in the wireless communication system.